It depends on measuring the changes in the impedance of a coil due to change in the flow of eddy current in a conductor. Any material change that affects the flow of the induced eddy current sufficiently can be detected. Because so many things affect the flow, eddy current inspection can be applied to a wide variety of test situations. Principle areas of application are flaw detection, material-thickness measurements, alloy sorting and the monitoring of metallurgical conditions such as hardness and heat treatment. Besides its versatility, the major advantages of eddy current inspection are the speed at which tests can be performed and its ability to inspect through painted coatings. It can be used also to inspect both ferromagnetic and non-magnetic materials. The principle disadvantages of the method is its limited depth of inspection into the material or part being inspected.